This invention relates to a method for reducing the surface charge of an ion exchange resin, to a method for reducing the agglomeration of the ion exchange resins in a mixed resin bed containing a cation exchange resin and an anion exchange resin and to the mixed resin bed exhibiting such reduced agglomeration.
In the deionization of water and other liquids, the liquid being deionized is often contacted with both anion and cation exchange resins to remove the undesirable ionic components therefrom. Although the contaminated liquid can be sequentially contacted with one resin type and thereafter with the other resin type, the liquid is more conventionally contacted with a resin bed containing a mixture of the anion and cation exchange resins, i.e., a mixed resin bed.
Due to the attraction caused by the oppositely charged surfaces of the two resins, the cation and anion exchange resins in such mixed resin bed often cling or clump together forming agglomerates of resin. Unfortunately, such attraction often causes difficulties in separating the cation and anion exchange resin into their respective resin types upon backwashing the mixed resin bed in preparation for the regeneration of the resins. In addition, resin agglomeration is characterized by the mixed resin bed possessing a relatively high void volume which often causes undesirable flow distribution of liquids through the bed, e.g., channeling, relatively low utilization of the resin's ion exchange capacity and a generally inefficient ion exchange operation.
Various methods have been employed heretofore to reduce the surface charge exhibited by the anion or cation exchange resin, thereby reducing the clumping of the resins in a mixed resin bed. For example, the prior art method of U.S. Pat. No. 2,961,417 proposes neutralizing the surface charge of the anion resin component of a mixed resin bed by treating the resin with an aqueous solution of an anionic resinous polyelectrolyte, e.g., a sulfonated polystyrene. Similarly, the surface charge on the cation resin is effectively neutralized using an aqueous solution of a cationic, resinous polyelectrolyte. In another method, the surface charge exhibited by the anion resin is neutralized by treating the resin with an emulsion of a pH responsive, swellable, cross-linked polymer bearing pendant anionic groups, e.g., carboxylic groups. Treatment of an anion exchange resin component of a mixed resin bed using either of these methods will reduce the clumping of the resins in said mixed resin bed. Unfortunately, however, the kinetics of the treated resin, i.e., the rate at which the treated resin can exchange the ionic components in solution, is also reduced, thereby lowering the overall efficiency of the mixed resin bed.
In view of the stated deficiencies of the prior art methods for neutralizing the surface charge exhibited by an ion exchange resin and for reducing the clumping exhibited by a resin bed containing a mixture of cation and anion exchange resins, it would be highly desirable to provide a method for effectively reducing the surface charge exhibited by an ion exchange resin thereby coincidentally reducing the clumping of the anion and cation resins in a mixed resin bed without affecting the resin's other properties.